Production of Excited Atomic Hydrogen from Methane

We have measured the production of Ly$\alpha $ and H$\alpha $ fluorescence from atomic H for the photodissociation of CH$_{4}$ by linearly-polarized photons with energies between 20 and 65 eV. Comparison between our Ly$\alpha $ relative cross section and that previously reported [1] show different peak height ratios. This also occurs in the H$\alpha $ cross section when compared to previous data [2]. We do not observe as significant a drop in either cross section above 35 eV. Our measurements were taken with pressures two orders of magnitude lower than those used in ref. [1]. We present comparisons between data sets and a discussion of possible systematic effects. [1] H. Fukuzawa \textit{et al.}, J. Phys. B. \textbf{38}, 565 (2005). [2] M. Kato et al., J. Phys. B. \textbf{35}, 4383 (2002). Support provided by the NSF (Grant PHY-0653379), DOE (LBNL/ALS) and ANSTO (Access to Major Research Facilities Programme).